Field of the Invention
The present invention relates to a laser processing apparatus for laser-processing a workpiece such as a wafer. More particularly, the invention relates to a laser processing apparatus suitable for laser processing of a single crystal substrate such as a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, a lithium tantalate (LiTaO3) substrate, a lithium niobate (LiNbO3) substrate, a diamond substrate, and a quartz substrate.
Description of the Related Art
In an optical device manufacturing process, an optical device layer including an n-type nitride semiconductor layer and a p-type nitride semiconductor layer is stacked on a surface of a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate or a gallium nitride (GaN) substrate, and optical devices such as light-emitting diodes and laser diodes are formed in a plurality of regions partitioned by a plurality of crossing division lines, to configure an optical device wafer. Then, the optical device wafer is cut by applying a laser beam along the division lines so as to divide the regions formed with the optical devices, thereby manufacturing the individual optical devices. In addition, a SAW wafer wherein SAW devices are formed on a surface of a lithium tantalate (LiTaO3) substrate, a lithium niobate (LiNbO3) substrate, a silicon carbide (SiC) substrate, a diamond substrate or a quartz substrate is also cut by applying a laser beam along division lines, thereby producing the individual SAW devices.
As a method for dividing a wafer such as the aforementioned optical device wafer or SAW wafer, a laser processing method has been tried wherein a pulsed laser beam of such a wavelength as to be transmitted through the wafer as a workpiece is applied to the wafer while adjusting the focal point to a position inside a region to be divided. The dividing method using this laser processing method is a technology wherein a pulsed laser beam of such a wavelength as to be transmitted through the wafer is applied to the wafer from the side of a one-side surface of the wafer while adjusting the focal point to a position inside the wafer, to continuously form a modified layer, which will serve as a starting point of breakage, inside the wafer along each division line, and an external force is applied to the wafer along each division line where strength is lowered by the formation of the modified layer, thereby dividing the wafer along the division lines (see, for example, Japanese Patent No. 3408805).
In addition, as a method for dividing a wafer such as a semiconductor wafer or an optical device wafer along division lines, a technology has been put to practical use wherein a pulsed laser beam of such a wavelength as to be absorbed in the wafer as a workpiece is applied to the wafer along the division lines, thereby to perform ablation processing and form laser-processed grooves, and an external force is applied to the wafer along each division line where the laser-processed groove is formed as a starting point of breakage, thereby cutting up the wafer along the division lines (see, for example, Japanese Patent Laid-open No. Hei10-305420).